The present invention relates generally to analog-to-digital converters and more particularly to an efficient analog-to-digital converter for digital systems.
Digital signal processors are becoming more popular, being used in a wide variety of applications including hard disk drives, cellular phones, modems and others. The digital signal processor typically operates on digital signals that have been derived from analog signals. The conversion from the analog signal to the digital signal is often performed by an analog-to-digital converter (ADC).
A number of techniques have been used to implement an ADC. For example, one type of ADC is the so-called parallel comparator type. In this device, an analog input voltage is applied to a number of comparators, the number being 2nxe2x88x921 where n is the number of digital bits to be generated. Each of the these comparators also receives a different reference voltage that ranges from near the highest voltage that can be expected to the lowest voltage that can be expected. The outputs of each of the comparators can be logically combined to generate the n digital bits.
One application that uses an ADC is a read channel of a disk drive. In this application, digital data is encoded and stored on a disk drive medium. The data must then be read from the drive and processed digital processing circuitry. An analog-to-digital converter is often used generate the digital circuitry that is processed by the digital processing circuitry.
The present invention provides an efficient analog-to-digital converter for digital systems. This analog-to-digital converter includes a number of advantages over prior art devices.
In a first aspect, an analog-to-digital converter includes first and second analog-to-digital converters both of which receive an input signal. The first analog-to-digital converter is configured to be centered around a first signal level point while the second analog-to-digital converter is configured to be centered around a second signal level point. A decoder receives inputs from the two analog-to-digital converters selected between the first analog-to-digital converter output and the second analog-to-digital converter output.
The concepts of the present invention can be utilized in a number of applications. For example, the read channel of a disk drive might include an analog-to-digital converter. Accordingly, the present invention envisions a novel disk drive system that includes one of the embodiment analog-to-digital converters described herein.
Different aspects of the present invention have advantages over prior art techniques. For example, since the analog-to-digital converter only performs fine resolution digitization at certain signal levels, the converter can be implemented with far fewer transistors. In one example, a prior art analog-to-digital converter that was implemented with sixty-three comparators can now be implemented with only twenty-one comparators. This reduction is the number of components also leads to a reduction in power consumption, a feature that is especially useful in mobile devices such as cellular telephones and mobile computers.